Asbestos has found extensive utility in the field of construction. Asbestos excels in weatherability and refractoriness and has enough formability to permit easy production of various shaped articles for a wide variety of applications.
However, it has been ascertained that the asbestos is a factor injurious to health. Thus, the use of this material has come to be substantially banned.
In the circumstances, there is a strong desire for the supply of a substitute with properties like those of asbestos at a low price.
The following materials are known as substitutes for asbestos.
Materials intended to effect reinforcement of building materials:
(1) Fibers such as of vinylon, acryl, nylon, polymethyl pentene, polypropylene, polyethylene, carbon, Aramides, rayon, and phenol. PA1 (2) Glass wool, rock wool, stainless steel wool, steel wool, gypsum, whiskers such as of potassium titanate, and ceramic fibers such as of alumina, alumina silica, and silica. PA1 (3) Such natural mineral fibers as wollastonite, sepiolite, and attapulgite. PA1 (4) Natural platelike materials represented by mica. PA1 (1) Natural materials such as of cellulose, pulp, rayon, and hemp and fibrillation products thereof. PA1 (2) Fibrillation products of synthetic fibers such as of polyethylene and polypropylene. PA1 Fine silica powder, silica hume, and extremely fine cement powder. PA1 Silica sand, calcium carbonate, etc. PA1 Polyolefins--Polyethylene, polypropylene, polybutene, and polymethyl pentene PA1 Other synthetic fibers--Polyvinyl alcohol, polyacrylonitrile, nylon-6, nylon-66, polyester, polyvinyl chloride, and polyamide PA1 Semi-manmade fibers--Rayon and acetate PA1 Natural organic substances--pulp, cotton, cellulose, wool, seed skin fibers, hemp, ramie, Manila hemp, flax, sisal hemp, mohair, and cashmere PA1 Manmade mineral substances--Slag wool, rock wool, glass fibers, carbon fibers, metal fibers, fibers of such ceramic substances as alumina, silica alumina, and silica, gypsum, and whiskers of potassium titanate PA1 Natural ores--Mica, wollastonite, zeolite, and attapulgite
Materials intended to improve building materials in formability:
Materials intended to improve building materials in strength:
Materials intended to increase volume:
Typical Japanese Patent Public Disclosures covering these materials are shown below.
Japanese Patent Public Disclosure No. 174343/1991 discloses a composition which comprises whiskers (such as of carbon, silicon carbide, silicon nitride, alumina, and potassium titanate) and an aggregate of particles having an average diameter not more than two times the diameter of the whiskers.
Japanese Patent Public Disclosure No. 114802/1991 discloses a method which comprises molding diatomaceous earth in the form of scales, converting the scales into pellets not more than 6 mm in diameter or rolling them to a thickness not more than 4 mm, mixing the resultant particles with portland cement and/or lime, fibers, and an extrusion auxiliary, adjusting the water content of the resultant mixture, and molding the mixture in a stated shape. It further discloses as fibers for use in the method described above inorganic substances such as asbestos, glass fibers, carbon fibers, and wollastonite, and pulp, polypropylene, polyvinyl alcohol, Kepler, and polyethylene fibers.
Japanese Patent Public Disclosure No. 141140/1991 discloses a composition which comprises polyvinyl alcohol type fibers or polyamide fibers and a synthetic pulp, wherein a study of the amounts and ratios of these components relative to the total amount of the composition enabled the composition to acquire improved ability of filtration as determined by a test for filtrability to water. It further discloses additives (such as, for example, mica, wollastonite, slag, silica, bentonite, and pearlite).
Japanese Patent Public Disclosure No. 54950/1985 discloses that the product obtained by preliminarily imparting minute grooves and ridges to the surfaces of fibers and subjecting the fibers to electroless plating thereby depositing such metal as Au, Ag, Cu, Ni, Co, Pd, or Sn on the fibers is used as a cement type reinforcing material.
The product resulting from the treatment just mentioned is expensive and entails both the step for imparting a rough surface and the step for plating.
Japanese Patent Public Disclosure No. 74546/1990 discloses that asbestos-free SiO.sub.2 --MgO--CaO--Al.sub.2 O.sub.3 type mineral fibers are produced by extrusion molding a mixture of cement, a siliceous raw material, and an extrusion auxiliary and that these fibers have a length of not more than 1 mm.
Japanese Patent Public Disclosure No. 69205/1990 discloses that the product obtained by preparing a composition of cement and silica, combining this composition with 8 to 13% of natural fibers of wollastonite or zeolite, and mixing the resultant blend with necessary additives, not including asbestos, is practically used.
Various known methods have been described. None of these methods, however, produces a material which equals asbestos in performance and is available as inexpensively as asbestos.
Vinylon, for example, possesses a hydroxyl group within the molecular unit thereof and consequently abounds in hydrophilicity and, when mixed with cement, thoroughly disperses therein. Since it is chemically active, however, it is deficient in stability. Polyethylene and polypropylene lack a hydroxyl group and do not exhibit high dispersibility in water. The idea of using a surfactant, for example, may be conceived for the elimination of these drawbacks. This idea, however, lacks practicability.
None of the materials developed heretofore is capable of substituting in its unmodified form for asbestos.
An object of this invention is provide a material which can be used in its unmodified form as a substitute for asbestos and is advantageously used particularly in civil engineering and construction grade materials.